Impression Evidence II

3D Impressions

3-D Impressions Impressed Evidence

Typically found in exterior surfaces Shoe deforms surface

Sand/soil/snow – other soft surfacesCharacteristics

Vary widely Shallow or deep Quality varies

Can have great detail or none

3-D ImpressionsValue of 3D Impressions

Impressions with sufficient detail can be associated with a specific item of footwear Impressions in clay-based soil

Can retain great detail Impressions in sand & small rocks

Little detail Dry packed snow

Greater detail than wet, melting snow

Collecting 3D Impression Evidence

SequenceDocumentation Sketching

Give lab knowledge where occurred @ sceneLab can recreate as closely as possible to original

o Differences in how recreated in lab v scene can affect making proper match

Field notes Photography

Necessary for court presentationCastingLifting

Most impression evidence has 3D characteristics … surface topography.

For forensic purposes, 3D impressions have depth in addition to length and width and commonly found outdoors in a soft or malleable receiving surface such as soil, sand or snow.

The quality (detail) varies with, The receiving surface’s malleability, texture and composition. The detail present in the source origin. The mode by which the impression was transferred to the

surface. The affects of weather: temperature, rain and snow.


Sequence

The scene investigator has no control over how the impression was generated or its clarity.

Responsibility: capture detail as completely and as clearly as possible. Two activities: 1. Photography and 2. Casting.

Casting defined:

“the filling of a three-dimensional footwear impression with a material that will acquire and retain the characteristics that were left in that impression by the footwear.”

Each archiving technique complements the otherPhotography and casting are not an either or decision. Both are critical and

both must be done in order to properly archive the impressions.


Sequence

Lifting & Preserving 3D Footwear Impression Evidence

What to CastIndented (Impressed) Dry

ImpressionsWet, 2D Prints on Concrete

Impressions in Snow

Impressions Covered by Water

Photography -v- CastingPhotography Casting

Shows impression as found at the scene Direct mold of the original impression

Condition and detail Reproduces microscopic characteristics

Can give best reproduction from coarse surfaces

Gives reproduction of sides of outsoles not reproduced in photographs

A backup for casting Backup for photography

Casting Footwear Impressions

Characteristics of Forensic Quality Casting Material

Produce very fine detailFlow easily into impressionCleaned without loss of detailEasily obtained with consistent quality &

propertiesEasily mixed – not require special equipmentSet in reasonable timeUnlimited shelf life

Quality of CastsReceiving surface malleability,

texture & compositionSandClayLoamy soil

Detail present in the impression Mode by which impression transferred to the surface

Mechanics of making the impressionEffects of weather:

Temperature Rain/snow Wind

Casting Gypsum manufacturing processes

CaSO4-2H2O 110-130 Deg C

GypsumCalcium Sulfate Dihydrate

(CaSO4)2-H2O 130-200 Deg C

PlasterCalcium Sulfate

Beta-hemihydrate

CaSO4 200-1000 Deg C

StoneCalcium Sulfate

Alpha-hemihydrate

Plaster of ParisRequires more water

Irregular Crystals & PorousConsistency > 50

AutoclavePressure

Steam

Open Oven

Dental StoneRequires less waterUniform CrystalsDense Crystals

Consistency < 50

Choosing Dental Stone

Regular plaster of Paris is 5,000 psi compression strength and will chip fairly

easily.

Hydrocal is around 8,000 psi and is more durable.

Merlin's Magic is around 14,000 psi and is even more durable yet.

Excalibur and Die-Keen are 18,000 psi and dry so hard it's almost like a ceramic

material.

Several kinds of dental stone … always check the compression strength measured in psi

(pounds per square inch).

http://www.hirstarts.com/casting/dental.html




Casting Footwear ImpressionsGypsum Consistency vs Compressive Strength (psi)

ConsistencyWater-to-Powder (W:P)

ratioLbs per 100lb plaster

Plaster per pounds of water

Dry compressive Strength(psi)

50 2lbs-0oz 3750

38 2lbs-10oz 7000

33.3 3lbs-0oz 9750

30 3lbs-3oz 11,000

21 4lbs-12oz 15,000

W:P – The quantity of water (by wt.) per quantity of powder (by wt.)A “30 Consistency” means – 30 parts of water/100 parts powderHigher the consistency – longer setting times – lower strength - softer

Mixing Merlin's Magic Merlin's Magic: Special type of casting material.

Made to pour into molds easily with very few air bubbles.

Mix differently than for regular plaster. Below are instructions to mix up enough plaster to fill one regular size mold.

First you need to make a measuring cup that can be reused.


Need two disposable plastic cups - nested. Pour 2 ounces (60 ml) of water into the top cup and place a black mark on the outside of the bottom cup where the water line is. Place an additional 2.5 ounces of water into the cup (for a total of 4.5 ounces or 135 ml). Place another black mark on the outer cup at the water line. Remove the inner cup and you have a reusable measuring cup.

Here is how you mix the plaster

Procedure for Merlin’s Magic

Insert a new cup into your measuring cup. Pour in water until it reaches the first line. Carefully shake in the powder until the mixture reaches the second line. The powder must be absorbed into the water before you can determine if the second line is reached. Remove the inner cup, mix up the plaster and pour it into your mold.

Mixing by weight,

Use table @ right. Need scale to measure the weight of the powder.

"ounces" shown here are a liquid measurement (not weight).

Mixing instructions on the package of Merlin's Magic will be different. Their instructions are used

for dental castings, which use a vibrator to shake thicker plaster into their dental molds, which can give mix that is too thick to pour into a mold.

Number ofmolds to fill

Ounces (or ml)of water

Amount of powder(by weight)

1 2 ounces (60ml) 186 grams




Casting Using Dental Stone

Photographing the Impression

Proper positioning of scales

Positioning of Retainer

Placing the casting frame in place

Mixing water (3/4 cup/lb stone)and dental stone

Pouring mixture onto impression

Curing the castAllow to sit 30-40 minutes before lifting

Do not remove adhering soil

Final cast Allow to cure up 24-48 hours Carefully remove soil Save Soil for comparisons

Casting Underwater Impressions

Drain or remove excess water – Good – BUT - Not Necessary Pipette or syringe Carefully Absorb with paper towel Pour casting material as usual

If water can’t be removed? Frame the impression Sift dry casting powder gently into water above

impression Allow to fall to bottom Sift until 1” of powder covers the areaPowder builds up & saturated with powderUse additional dental stone slurry to fill the framed area

Will settle into the water later & into impression – cover entire impression

Allow to set for at least 1 hour

Casting in SnowCasting Procedure

Spray Impression with Snow Print Wax or Dust with Snow Print Powder 2-3 layers

Allow to dry for 2-5 minutes between applications

Slowly Add slightly cooled dental stone

Cooled dental stone minimizes melting the snow

Non-Casting Procedure Auto primer spray paint before

Snow Print Better contrast for

Photographs Photos critical

Can’t directly cast with primer paint

Many snow prints not cast

Spray the impression lightly with the Snow Print Wax at an angle in order to highlight the raised areas of the impression. Do not cover the entire area of the impression. This is the best time to

photograph the sprayed impression. Do not hold the spray too close to the impression because the blast from the

aerosol can damage the impression’s detail. Spray the impression with 2 or 3 more applications, ensuring that the entire

impression is covered in wax. A properly sprayed impression will not reveal much detail when viewed from above.

The red (or other colored sprays) attracts heat: Shield the impression from the sun.

Allow the wax mold to dry for approximately 5-10 minutes. Prepare a dental stone slurry and allow it to sit longer than usual so that when the

slurry begins to harden, the heat generated will not melt the impression. When the cast is hardening, scratch initials and date into the cast. Allow the impression to sit for approximately 60 minutes before lifting.

After lifting, immediately photograph the cast. Snow print casts are fragile, and the wax molding is easily destroyed. Keep the cast

away from sunlight. If melting occurs, cast detail may

Snow Casting Procedure

Snow Print Wax

Casting with plaster

3D surface scanning

3D model of the sole

GOM ATOS II system (Gesellschaft fu¨r Optische Messtechnik mbH, Braunschweig, Germany).

3D Scanning

http://cs.iupui.edu/~tuceryan/pdf-repository/Buck2007.pdf

Packaging Casts

Allow cast to dry for 24 hours or longer Do not attempt to remove soil or clean until cured

Will destroy impressionSoil used for comparison purposes

Loosely & individually wrapped in paper or paper bag Do not wrap in tight plastic

Place wrapped cast in cardboard box & tape seal

Place in shock absorbent or porous packaging material

Identification:

Before cast hardens, place CSI or investigator’s initials, date and case & number on back side of cast.

Amount Desired: Standard -Evidence - Up to 2 ft.

Preservation: Use mesh reinforcing and let dry 24 hours before putting in package.

Wrapping & Packing: Surround with packing material in box too prevent

shifting or breakage. Avoid sealing in plastic bags.

Miscellaneous: Dental stone is the preferred casting material. Take

photos of impressions before casting. Mark package FRAGILE. Do not clean.

Do not use twigs for reinforcement.

Illinois State Police Packaging Procedure for Cast Impressions

http://www.isp.state.il.us/docs/6-420.pdf

Impression Evidence On-Scene Overview

[1] Adapted from Hilderbrand, Dwane S. Footwear, The Missed Evidence, Skaggs Publishing 1999, pages 61-62.

Impression[1]

And SurfaceCategory

of Impression

Archiving Method

Enhancement Method

Preservation Method

Wet soil or Mud (fine, even consistency)

3D Photograph 1. Dust with black/fluorescent or bicolor magnetic powder

Cast using dental stone

Concrete 2D Photograph quickly

1. Quickly dust with black/fluorescent or bicolor magnetic powder

1. Re-photograph2. Cast using dental stone

In dry soil (Hard, packed or loose. Varying in consistency from coarse to powder-fine)

3D Photograph 1. Stabilize with hair spray or lacquer2. Spray with automotive primer paint of appropriate contrasting color


Sand(variable texture – retains small amount of impression detail)

3D Photograph 1. Stabilize with spray paint (black) or “snow print wax” or “snow print powder”2. Spray with automotive primer paint.


Impression[1]

And SurfaceCategory of Impression

Archiving Method

Enhancement Method

Preservation Method

Snow(Temperature affects textures, cohesiveness and impression detail)

3D Photograph 1. Stabilize with automotive primer paint (gray) and/or “snow print wax or powder”2. Spray with automotive primer paint.

1. Re-photograph2. Cast using dental stone or Jade Stone

Dry Residue - Dust on Hard Surfaces(Produce highly detailed impressions on hard surfaces)

2D Photograph 1. Lift using electrostatic or gelatin lifter) 2. Chemical enhancement.

Re-photograph

Wet Residue – Dust or Mud on Hard Surfaces(Highly detailed impressions)

2D Photograph 1. Cannot be lifted using electrostatic lifter. Can be lifted using gelatin lifter2. Dust with magnetic powder (dual color or black)3. Treat for the presence of iron or other metals4. Cyanoacrylate fume followed by powder dusting or fluorescent staining (surface dependant)

1. Re-photograph2. Lift with gel lifter

Dust – Fabrics(Carpet, upholstery & bedding can produce detailed impressions within the fabric nap or on the surface)

2D Photograph 1. If dust – lift as above. 1. Re-photograph2. Cast using Jade Stone … or3. Lift with gel lifter

Blood(Can produce high-detail impressions)

2D Photograph 1. Light surfaces – Stain using Acid Violet 17.2. Dark surfaces – stains using Basic Yellow 7 or DFO.

1. Re-photograph2. Lift using gelatin lifter.

Exemplar Impressions

Exemplar Footwear ImpressionsMany people leave impressions @ scene

Categorize designs of shoesVictimsWitnessesMedical personnelOther innocent peopleOfficersSuspects

Known impressions made Specialty impression materials available

Biofoam

http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

Gellifter

Inkless Lifter

http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

Forensic Footwear DatabasesTreadMark™

The number of shoe prints at a crime scene can be so large that the process of impression recovery becomes very time-consuming.

Commercial product using four parameters—pattern, size, damage, and wear—to identify individual outsole impressions.

Compared with shoe print data from two sources: suspects in custody and crime scenes.

A match could yield the name, date of birth, criminal record number, places of interest, and similar offenses for possible suspects.

How does TreadMark™ work?

Impressions from crime scene obtained using photograph, gel lift, dust lift, and adhesive lift.

Input directly into the analytical system by high-resolution digital imaging. Same procedure used with impression of a suspect’s shoe print:

Operator measures, analyzes, and compares crime-scene and suspect images.

Both image sources can be searched within themselves and against each other, allowing such images to be transmitted to other users.

www.csiequipment.com/systems.aspx Exit Notice.

http://www.csiequipment.com/systems.aspx

http://www.justice.gov/legalpolicies.htm

SoleMate Commercial database contains information—manufacturer, date of market

release, an image or offset print of the sole, and pictorial images of the uppers—for more than 12,000 sports, work, and casual shoes.

Sold on DVD, updated and distributed to subscribers every 3 months.

Limitation is that different manufacturers often use the same sole unit. Therefore, it may be difficult to determine the exact make and model of a shoe. The software links such records, however, so that all footwear that might match a crime-scene print can be considered.

How does SoleMate work?

The pattern of an unidentified shoe print is assigned a set of codes to isolate basic features, such as circles, diamonds, zigzags, curves, and blocks. Options, with variations, are presented pictorially, allows investigator to code features that best match the shoe print.

These codes form the database search, with results presented in descending order of pattern correlation.

Foster & Freeman USA Inc., at 888-445-5048.

http://www.fosterfreeman.com/

http://www.fosterfreeman.com/

TreadMate

Maintained by the same United Kingdom company that markets SoleMate, this database contains information:

5,000 vehicle tires and tire tread patterns, Manufacturer, Date of market release, Pictorial image, Pattern features.

Because manufacturers sometimes use the same tread, it may be difficult to find the exact make and model match of a tire. In these cases, records are linked so that all tires that might match a crime-scene tire mark may be considered.

How does TreadMate work?

The pattern of an unidentified tire mark is assigned a set of codes for pattern features, such as waves, lines, diamonds, zigzags, curves, and blocks, which then form the basis of the database search. Results are presented in descending order of correlation.

Foster & Freeman USA Inc., at 888-445-5048 or [email protected].

mailto:[email protected]

Tire Print Evidence

Evidence Often Overlooked

Vehicle-involved scenes run the gamut of scene types: homicides, sexual assaults, burglaries, drive-by shootings, terrorist events, etc. Identifying vehicle should be a critical aspect of any on-

scene investigation.

In typical homicide investigation, investigators must consider the possibility that specific categories of physical evidence related to the crime are present. Hit and run crimes, whether vehicle-vehicle, vehicle-

person, vehicle-other object, involve vehicles that leave the scene.

In these crimes, damage creates physical evidence Evidence could prove the culprit vehicle was at the

scene; o This evidence should be collectable.

Vehicle-Involved Scenes

The following article from the New York Daily News is such an example[1]. In this case, the suspect and his vehicle were found. The NYPD crime scene unit had the responsibility of working the car to prove it was the vehicle that struck the victim.

The abducted child case. No evidence found inside the suspect vehicle proving the child there … Must consider other, indirect, avenues to move investigation forward.

The abductor vehicle had been at the scene. Success includes thorough investigation of the outside where the vehicle

might have been parked Physical evidence collected and scene archived.

One example of physical evidence vehicles leave behind is tire track impressions.

Hypothetical - Kidnapping Involves a vehicle for transport Critical to find physical evidence that the child had been inside the car, Reality: Such evidence may not be present or had been removed.

Case ExampleKidnapping

Tire Track Impression Evidence Evidence Often Overlooked

Footwear Impression: Dealt with locating, enhancing, photographing, etc, footwear impression

evidence, Much of that discussion is applicable to tire track evidence as well.

Similarities with Footwear Impressions Tire track evidence:

Classified as two-dimension (2D) or three-dimension (3D). Commonly in dust or are otherwise contaminated 2D impressions or

impressions in a soft surface. Considered Class or individualizing:

Physical characteristics needed for meaningful criminalistic-quality comparisons

Former provides information about the tread design Latter provides information imbedded into the tread of the tire from daily

usage.

Provides evidence of the individual (shoe impressions) or the vehicle (tire impressions) being at the scene, For tire tracks, suggests the individual vehicle was

used in the crime. Tire track impressions geared to identify vehicle …

not the person, Although the person might have been driving the

vehicle.

Footwear & Tire Track DifferencesTheir Intrinsic Forensic Values

How Important is Scene Evidence?

Identifying specific vehicle requires recovering it and making direct comparisons with physical evidence from scene Scene data allows investigators and laboratory

analysts to narrow the search among universe of vehicles.

Until suspect vehicle is located and impounded, all scene data must be archived, collected and preserved. Determining which tire tracks to photograph,

enhance and or cast is critical

Critical Vehicle InformationCrime Scene Procedures

Direction of travel Relationship of impressions

@ scene to arrangement of tires on suspect vehicle

Position of front of vehicle Which impressions made

by front & rear tires Which impressions to

photo/cast Locations where vehicle

track measurements will be recorded

Other relevant evidence Footwear impressions Fluid spills

How vehicle was maneuvered?

Vehicle characteristics Stance Track measurements Wheelbase Tread wear

indicators Wear bars

No. vehicles & no. occupants

Were objects loaded or unloaded?

On-Scene Considerations

Unknown: Whether something seemingly unimportant and ignored

will be important as evidence AND suddenly plays a prominent role in the investigation. Consider everything at vehicle-involved scenes as

potentially probative. Misperception that tire track impressions have little

forensic or investigative value. General scene investigative principles apply equally to

vehicle-involved scenes; Management, archiving, searching, etc, are an integral

aspect of the investigation.

Success At the SceneOne Shot at It

Crime Scene Procedures

Official Busines

s

Scene&

Command Center

Official Busines

sSegregatedWitnesses

& PotentialSuspects

Media

Discrete Security Areas at the Scene

Public Public

Secure Travel Routes for Emergency Equipment / Personnel

Secure the area Tire prints protected

Obtain information Case information Vehicle information Scene information

Establish safe path to view evidence

Archive

Collect/package/preserve evidence

ManagementShould employ guidelines

previously discussedWhile these principles are

inviolate Unique characteristics

for vehicle-involved scenes. Specifically,

identifying, archiving, characterizing and preserving the physical evidence associated with identifying a suspect vehicle.

Investigative Questions Archiving Sketching and critical on-scene

measurements Vehicle information Suspect information Reconstruction

Archiving

Photographing, sketching, video, 3D-Imaging tire-track and other vehicle-involved scene evidence

Much like for footwear impression evidence.

For tire track impressions – Document at least 24” of impression

For comparison purposes

Archiving

Photography of Tire Track Impressions.

Photos must Include markers that Identify the tire position on vehicle

– Establishing or Overview Photographs• Tell the story and relationship of how the tire tracks relate to the overall

scene. Photos with and without evidence markers in place.

– Midrange• Tell the story of how the tire track evidence relate to each other and to

nearby objects. Photos with evidence markers are important to establish evidence-to-evidence relationships.

– Close-ups• These include at least 24” of all 4 impressions, appropriately identify

which tire, e.g., right front, etc, being photographed. Photos with and without scales must be included.

Considering Lighting and Glare3-D Impression

Blocking Sunlight Using Ambient Light

Photographing 3-D Impressions Photograph before casting Reproduces class characteristics

Accidental characteristics are often lostSpray paint may enhance sufficiently

Outdoor lighting may make it necessary to block direct sunlight Sometimes sunlight may be superior to oblique

lighting Use polarizing filters to eliminate glare

Look for sidewall information in impression

Photography – Effect of Lighting

• Existing light blocked out and oblique light provided with off camera Flash

Archiving 3D ImpressionsCasting

http://projects.nfstc.org/ipes/presentations/Bodziak_Footwear-Non.pdf

Archiving 3D ImpressionsCasting

Tire Impressions in the SnowReverse Sidewall Impression

Marking Tire Impression EvidenceVehicles Still at the Scene

Photographer’s name, Date, Time Use scales in plane of impression Mark tire position on vehicle & on scene

Use spray fluorescent paint for all wheels Rt front, etc

Arrow pointing to front of vehicle Establishes inside & outside edge of impression

Impression number 1st or 6th impression recorded @ the scene

N/S directional

SketchesTire Track Impressions

Plan sketches: Overview of impressions In-Depth detail not important

Measurements Photography

Sufficiently detailed to permit a determination of specific vehicle characteristics

Dependent on the amount and detail of the tire track impressions present.

Appropriate measurements must be made. The measurements are the critical data

needed to compare the on-scene tracks with a suspect vehicle.

Archiving – SketchesInclude Vehicle-Critical Measurements

Anatomy of the Tire

http://www.jacks-tire.com/Tire101.aspx

Tread Design

PitchEliminating Road Noise

SmallLarge Medium Medium Small

Vehicle Information

How Was the Vehicle Maneuvered?

Closely examine tire tracks

Using known factors

Common sense

Direction of Travel

Direction of Travel Spinning tires Striations by sidewall in furrow

Shows which way tire rolling Location where vehicle stopped,

backed up to change direction Overlapping front & rear tire

tracks Look to see if coming or going

from scene Grass or small plants

Direction they were flattened Directional tire tread patterns Damp soil or snow

Tires lifted soil or snow slightly in direction of travel

Deposition of transferred material in direction of travel

Mud, dirty water or fluids splashed or thrown in direction of travel

Make the Appropriate Tire Track Measurements

Wheelbase Front track width Rear track width Turning diameter Tread design width (arc width) Tread depth (skid depth) Tire circumference

Front Tires Turned

Front TireTrack Width

Rear TireTrack Width

ApproximateWheelbase

WheelbaseDefined as the distance between the leading edge of

the front and rear tires.

WheelbaseFront Wheels Turned

Inside leading edge of track will be rounded Make rt. Angles to center

line of impressionWill run laterally across

the width of impressionProject line along inside

edge – parallel to center lineo Intersection is fixed point

on inside leading edgeo Repeat of all 4 tires

Wheelbase in Mud & Snow

Camber

http://en.wikipedia.org/wiki/Camber_anglehttp://autorepair.about.com/od/glossary/ss/def_camber.htm

Camber Tilt” of the tires as they

rest on the ground.

Mechanical issues with vehicle affect how impressions appear at scene

Differences between normal and abnormal camber (positive or negative) signifies

improper alignment or worn front-end parts of the vehicle.

Positive camber: tires tilted further apart, “out,” at the top.

Negative camber tires tilted closer, “in,” at the top,

Normal Camber

Positive CamberTire tilted “out” @ top

Negative CamberTire tilted “in” @ top

Narrower

Wider

Track Width or Stance

Front and Rear Track Widths

• Track widths– Midpoint of leading edge of

front and rear tire track impressions

Front TireTrack Width

Rear TireTrack Width

Front and Rear Track Widths

Defined as distance between middle of leading edge of the front and back tires.

Mechanical issues can affect how these impressions appear at the scene.

Among others, one is camber, which is the “tilt” of the tires as they rest on the ground.

Toe Difference between

front & rear of front tiresNormally set “in”

only a few millimetersoCompensate for

normal front end tendency to toe “out” at highway speeds.

Improper alignmentWorn front end

components

Track Width Toe In or Out

Vehicle InformationTurning Diameter

Diameter is defined as the diameter of the circle made when the vehicle is driven in a circle.

Determined from measurements taken @ scene.

Turning diameter

Turning Diameter

A AA

B

C

Front Tire

Rear Tire

Calculating Turning Diameter

On-Scene Tire Impression

BD Bisects A – AA @ C: Line E= Distance B to CDistance C to AA = Line F (= distance A to C)

Turning Diameter = (F / E) + E (11)Alternatively: Turning Diameter = (F /8E + E/2) (12)

EF

22

At the scene Don’t know if the turn is full-lock Curb-to-curb for the outer tires

Not wall-to-wall for outside edge of vehicle

Procedure Select segment reflecting

sharpest portion of turn Measure imaginary line

between 2 points of arc Measure outer margin to outer

margin A-AA

Bisect line & draw line to outer margin of track arc –

(A-C) Draw another line between the

bisect point and the inside of the track arc –

(C-B) Calculate diameter

Approximate the tire circumference by finding an accidental, repeated characteristic, such as a gouge or cut, along the imprint. The distance between these repeated marks is the rolling tire circumference.

Investigators must understand that measured value – accidental characteristic-to-accidental characteristic – different from value obtained by wrapping the measuring tape around the tire in its center line, Larger

Procedure

Measure distance between repeated accidental characteristics on impression Considerations

Measured value is less than when the tape is wrapped around the tire o Tires have a curved arc width, impressions do not.

Measured circumference is larger in the center line of the tire than at the outer edges.

Tire circumference

Vehicle InformationTread Design

Tread design width:

Measurement from one edge of the design to the other.

These measurements must be measured at the scene from the impression.

Information important so manufacturers can help investigators identify an unknown impression.

Tread design width (arc width)

2D impressions visible because of contaminants adhering to the tread; dirt and dust the most common. Other contaminants also create impressions

water, grease (oil) or blood. Each leaves visible impression Each can be enhanced, depending on the contaminant.

Consideration of Enhancement Choices Variety of choices and investigators must make the proper decision.

Archiving the impression photographically is step-one Enhancement choices and the variables offered by the scene:

o Surface material, o Chemistry of the impression material (dirt, oil, blood, etc), and

the o Chemistry of the enhancement method.

Non-dirt Impressions

Tread Wear

Tread Wear Indicators

Tread wear indicators (wear bars) Located in grooves of tread design

Run laterally across treado 1/16” above base of the groove

Useful for comparison purposeso Divide tire into useful segments

Cars & light trucks 6 evenly spaced

o Rim diameter of 305mm/12 inches must have @ least 6

o Less than 305mm must have @ least 3/12 inches

Wear Bar Indicator

Tread Wear

Tire wear indicator

First thousand miles produces the fastest tread wear

As elements become shorter Flex less & squirming is reduced Slows considerably Accidental characteristics last

longer on well-worn tire than on a new one

Factors Affecting Tread WearExcessive under-inflationExcessive over-inflationBalancingImproper toe-in-outImproper camberChunkingFaulty breaksCombined suspension

steering issuesBad repairs

Equipment: Tread depth gauge (Measures in 1/32nds) or

15mm ruler Newer tires: 11/32 to 16/32”

Maximum depths suggest newer tiresWear bars are set @ 2/32nds, Wear patterns appear as solid bar in the

tire impression

Procedure Estimate height of groove in scene

impressionSet depth gauge on impression grooveCarefully lower gauge into impression &

read depth from the scale Alternatively, measure depth from cast in

dental stone

Measuring Tread DepthNon-Skid Depth

When tires near end of life, U.S. Lincoln penny can be used to confirm the tire's tread depth. If Lincoln's entire head is visible, the tire is worn to approximately 2/32" and is

considered legally worn out in most States. Average new tires used on cars typically start with 10/32" to 11/32" of original

tread depth. Dedicated winter / snow tires and light truck tires typically are deeper - how much

deeper depends on tire's tread type ... Highway Rib, Highway All Season, Off Road All Terrain or Off Road Maximum Traction). Means - original tread depth has only 8/32" of useable tread depth. Useable tread depth calculated by subtracting a worn out tire's 2/32" from the

new tire's original depth of 10/32". The final 2/32" of a tire's tread depth isn't part of the equation when it

comes to calculating tread depth percentages because the tire is already legally worn out.

Remaining tread depth used to calculate tread wear percentages. … o Tire that started with 10/32" of original tread depth and has worn off

4/32" (down to 6/32" of remaining tread depth) is 50% worn.o 2/32" legally worn out tread depth

A tire that starts with 10/32" of original tread depth has 12.5% wear for every 1/32" that is worn away, and a tire that starts with 12/32" " of original tread depth, has 10% wear for every 1/32" that is worn away,

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=197

Tread Depth - Some Statistics

Identifying Tread Wear

Exposed tire bars Tire bars recessed in

sipes & grooves become exposed

• Circular wear Wear around

circumference w/sipes & grooves indicates wear

2/32 TreadLegally Worn

4/32 Tread

6/32 Tread

Enhancing Tire Tracks

Involves many of the same principles as for footwear evidence Photography :

A method for archiving AND enhancing. Chemical enhancements.

Chemical treatments take advantage of the inherent chemical signature of the impression o Minerals, such as iron and aluminum, etc,

organics, or bio-materials – to more clearly visualize the impression.

The chemical enhancements are essentially the same those used to enhance footwear evidence.

Enhancing Tire Track Impressions

Chemical EnhancementMetals in Soil

Impressions with Metals Ammonium or

Potassium Thiocyanate Tests for Iron

Reddish brown 8-Hydroxyquinoline

Iron, magnesium + other metals

Fluorescent under UV light

Impression w/oil or fats Iodine fuming or Iodine

crystals Oils & Other organic

compounds Iodine absorbed

Enhancement Benzophenone

o Forms stable blue color

Thin layer of starch powdero Subsequent steam

treatment turns starch blue

Chemical EnhancementWet Tires with Salt Deposits - Winter

• Silver Nitrate– Converts NaCl (salt) to AgCl (Silver

Chloride)• NaCl + AgNO3 AgCl + AgNO3

Ag Metal– UV or sunlight darkens impression

hvRoad Salt2% Silver NitrateIn Methanol

Tire Tracks in BloodChemical Enhancement

Blood reactive chemicals DAB Leucocrystal Violet Acid Violet 17 Acid Yellow 7 – dark surfaces – yellow fluorescence Amido Black Ninhydrin DFO Crowle’s Stain TMB Coomassie blue Nile Red Hungarian Red Ashley’s reagent

Investigative EvidenceIdentifying Unknown Vehicle

Tire Impressions as Investigational Aids

Identifying manufacturer & brand name Done after processing the scene Tread design

Who makes it & where Tire guides – Boca Raton, FL

Shows tread patterns for all types of tires sold in the U.S.

Comprehensive Visual Identification of all types of Tire Tread Pattern Designs.Covers Passenger, Light Truck and Medium Truck vehicles. Includes Off-Road and Agricultural Tread Patterns. Also covers Motorcycle and retread tire tread designs. Provides information on how to read a tire sidewall and on the different Tire

Sizing Systems. Gives detailed information on Speed-Rating and Load Indexes as well as lug

nut torque and tightening sequences. http://tireguides.com/Products/245

On-Scene InformationLimited Slip Differential (LSD)

Posi-tractionOne wheel was spinning

o Movie: My Cousin Vinnieo Can narrow type of vehicle

Odd mixture of worn tires Suggests an older vehicle

Possible alignment problemsStolen items - gasoline

Location of gas tanko Check footprints @ side of car where gas tank located

Estimate from amount taken whether a truck (pickup-SUV)

Mechanical Problems

Mechanical Problems & Vehicle Design Features

Fluid leaks @ scene Oil, antifreeze, brake fluid, trans fluid

Collect for chemical analysis @ lab

Vehicle Location History

Foreign Material on Suspect VehicleNotice unusual material in tread

impression Collect & take to lab

Identifying The Correct Impression

Age of Tire Impression How Long @ Scene

• How long an object (driven over) has been lying on the ground– Complainant may have this information

• Transferred substance– Recently spilled Fluid

• Knocked over objects• Weather conditions prior to offense

– Help date time of deposit of scene impression

Known Tire Impressions

Known Tire Impressions

Need one full circumference of the tire

Complex pitch in modern radials

Might miss important accidental characteristics

Taking Tire ImpressionsMethods & Materials needed

Large area to make impression

Broom Vehicle lift Tire marking crayons Rag to clean dirt

from tires Roll of paper towel Large jar of

Petroleum Jelly (Vaseline)

Gloves Art board 15” x 40” (3

pieces/tire)

Lg & sm felt marking pens

Magnetic jet black print powder

3” wide magna brush Strips of polyester

plastic 12” x 40” to protect impression

Scotch tape to attach plastic to art board

Information From Each Tire

• Photograph Tire– Exterior sidewall– Tread design– Serial number – Design, mold &

drawing numbers• Show up after

rubbing w/crayon

• ID each tire later– Manufacturer– Tire brand name– Tire size– Type of tire

• Summer, etc– Construction

• Radial, bias ply, etc– Other numbers

• Mold, design, etc– Wear– Number of ribs in design

Recording Known Tire ImpressionsRecording known tire impression

Art board is superior to paper Small debris on surface

can’t come through Reduces/eliminates

wrinkles/tearing common with paper

Use gloves to keep board clean

3 pieces of 40” Board sufficient to record 1 full circumference of tire

Tread Wear Indicators

Recording Known Tire ImpressionsPetroleum Jelly/Magna Brush Method – 2D

Place 2 pieces of art board in path of vehicle travel Tape on reverse side to

hold pieces together Mark adjoining pieces

appropriately Push car over recording

surface Vaseline leaves light

brown impression Mark on art board as

each tread wear indicator (marked on sidewall) rolls by

Mark spaces on art board to correspond to numbers on known tire Tire Wear Indicator Marks

Place locations on sidewall

Recording Known Tire ImpressionsPetroleum Jelly/Magna Brush Method – 2D

Cover art board in front & behind impression w/paper towel to protect it

Clean area of tire that was on the floor when Petroleum Jelly first applied Apply Petroleum Jelly to this area and push

car again

Recording Known Tire ImpressionsVaseline/Magna Brush Method – 2D

Near end of second art board Stop vehicle Remove 1st piece of art board Add thin coat of Vaseline to tire Place 3rd piece of art board in path of vehicle

Continue pushing until known impression is transferred to this 3rd section

Recording Known Tire ImpressionsPetroleum/Magna Brush Method – 2D

• Dust impression as soon as possible– Waiting too long causes defined areas of

tread to diffuse into art board surface• Brush with magnetic brush @ rt. Angles

w/swirling action– Avoid dusting clear areas of board– Black magnetic Dusting Powder

Recording Known Tire ImpressionsVaseline/Magna Brush Method – 2D

Protecting the impression Cover with clear acetate to prevent smearing or

damage during transit & comparison processAllows examiner to draw lines during comparison

Recoding Known Tire ImpressionsInking Method I

Apply ink to art board for 1 full circumference Fingerprint Ink works

Push car (tire) over inked art board This is the inking process

Push car over clean strip of white art board to record the impression

Recording Known Tire ImpressionsInking Method II: Transparent Method

Ink the tire as in inking method

Drive tire over transparent acetate or other transparent media (Mylar) Tape to art board - suitable solid backing

Advantages Can be rolled up for storing Unrolled @ later time for comparison Can be compared directly to impression when

searching for

Comparing Scene Cast with Acetate Exemplary Overlay

The area defined by blue tape isthe segment of the right reartire which corresponds with thecrime scene cast.

Comparing Scene Cast Actual Exemplar Tire

Impression Evidence II

Documents

Transcript of Impression Evidence II